The present invention broadly relates to an improved electrolyte and process for electrodepositing zinc, and more particularly, to an improved non-cyanide acid zinc electrolyte containing improved carrier brightening agents.
A variety of aqueous cyanide-free acidic zinc electroplating solutions and processes have heretofore been used or proposed for use. In many instances, such acid zinc electrolytes contain polyalkoxylated nonionic surfactants as carrier brighteners in further combination with primary and supplemental brightening agents to achieve a zinc deposit of the desired characteristics. A continuing problem associated with the use of polyalkoxylated nonionic surfactants as carrier brighteners in prior art electrolytes has been the tendency of such electrolytes to reach a cloud point at relatively low bath temperatures, such as about 80.degree. to about 100.degree. F. This problem is further aggravated when the acid zinc electrolyte contains relatively high concentrations of soluble constituents, particularly dissolved metal ions of the periodic table of Group I and II metals as well as ammonium ions. The operation of the bath at relatively high current densities also contributes toward an increase in the temperature thereof further aggravating the tendency of such carrier brighteners to attain the cloud point. When the cloud point of the nonionic carrier brightener surfactant is attained, the carrier brightener is rendered inoperative and no longer contributes to a brightening effect of the zinc electrodeposit nor does it function secondarily as a surfactant to emulsify oils and other organic contaminants in the electroplating bath.
The present invention overcomes the problems and disadvantages associated with prior art acid zinc electroplating baths by employing an improved anionic surfactant carrier brightener having a substantially higher cloud poit which is compatible with other conventional primary and supplemental brighteners of the types conventionally employed achieving the same benefits as heretofore provided by nonionic carrier brighteners while at the same time substantially increasing the flexibility of operation of the bath to obtain zinc electrodeposits of the desired quality.